The present invention relates to the use of alkali fluorostannates, particularly potassium and cesium fluorostannates as a brazing or soldering fluxing agent or as a constituent of brazing or soldering fluxing agents for components made of aluminum and aluminum alloys, and to new fluxing agents which contain potassium and/or cesium fluorostannate or are made thereof.
Assemblies (for example radiators for automobile engines or heat exchangers) may be manufactured from aluminum parts or parts made of aluminum alloys through brazing (hard soldering) or soldering (soft soldering). For this purpose, fluxing agents based on potassium fluoroaluminate are used. The surfaces of the components to be brazed or soldered to one another are freed from oxidic adherents using these fluxing agents. Such a method is disclosed in British Patent 1 438 955. The production of corresponding fluxing agents is, for example, described by Willenberg, U.S. Pat. No. 4,428,920 and Kawase, U.S. Pat. No. 4,279,605. Fluxing agents which contain cesium fluoroaluminate and possibly also potassium fluoroaluminate are particularly suitable for brazing or soldering aluminum alloys having a higher magnesium content, see Suzuki, U.S. Pat. No. 4,670,067 and Shimizu, U.S. Pat. No. 5,171,377. Instead of a solder metal, a metal which forms a eutectic mixture with the aluminum upon brazing or soldering may also be added to the fluxing agent. Such metals include, for example, copper, zinc, and germanium, and particularly silicon.
The use of solder metal may be completely superfluous if specific metal fluorosilicates are added, see European Patent Application 810 057 and WO 98/10887. In the latter patent application, it is disclosed that a solder metal may be dispensed with if a mixture of potassium fluoroaluminate and potassium fluorosilicate, which contains potassium fluorosilicate in a quantity from 6 to 50 weight-percent, is used.
Finally, using fluxing agents which contain alkali metal fluorozincates is known, see International Patent Application WO 99/48641. In this case, a zinc layer which protects the surface against corrosion forms on the components.